3.8l Vs 4.1 ?

[Arji]

Want to restore my 1st ever car. I have to replace the motor.
I read eighty2regal's post and it mentions the 4.1 (mine orriginally had the 3.8 turbo but has nothing now )

Since I am looking for a new motor anyway, should I be looking for the 4.1, or stick with the 3.8?

Will the 4.1 even fit my car/transmission? (I have a 81 regal sport coup)?

In short, wich is the better engine?

 

[Freddie's Buick]

Rich will probably have the best answer for ya..But from what I've heard the 4.1 will drop right in. (And the tranny fits also).

Do you have the original transmission? If you don't, then you'll probably need a THM-350C transmission. If I were you I'd get the 3.8 turbo. Even a junked one should be bought and rebuilt since they're very rare and will be much harder to find with time.

 

[b4black]

All Buick V6's are very similar. The basic motor you are interested in is the RWD version from 1979-1987. They come in three "levels".

3.8 NA (for normally aspirated), 3.8 Turbo and 4.1

3.8 NA's are the most common and all had 2-barrel carbs from the factory. (All 4.1's had 4-barrel carbs.)

3.8 Turbos have the same bare block and heads. The crank and psitons are stonger and the cam is different. And them there is all the turbo specific bolt-on stuff.

The 4.1 is identical to the 3.8, expect the bore and pistons are larger. The 4.1 is a direct replacement for a 3.8. The crank is the same as a Turbo V6, but the pistons and cam are more comparable to the 3.8 NA's.

The Turbo V6 is the most durable. But any 3.8 NA and 4.1 can be rebuilt to the 3.8 Turbo's strength.


IF you plans are to keep performance to factory specs, and you don't plan on pushing the engines limits, the Turbo V6 engine is overkill. A 3.8 NA spec motor can handle the turbo's power. Even GM will sell a rebuilt 3.8 NA for 1978-83 Car/Turbo applications with a warrenty. Many Turbo V6 motors are replaced with NA motors. (Both my GN's have them from previuos onwers.)


In your situation, I would start be getting a decent junkyard 3.8, or better yet a 4.1. Install it as is, without the turbo and get the car running. Then start collecting the right Turbo stuff. And keep your eyes open for a running parts car.

 

[83T]

Hey Rich,

Keep on thinking of the 4.1 myself (my car has 50,000 on it since I built the motor under two years ago, and at this rate am starting to think of rebuild time again) Do you think a properly rebuilt 4.1 (with the correct rods and crank) could handle the power of the turbo setup? My setup would be the same other than that and having the turbo hogged out.

Rick

 

[Schlodes]

Originally posted by 83T
Hey Rich,

Keep on thinking of the 4.1 myself (my car has 50,000 on it since I built the motor under two years ago, and at this rate am starting to think of rebuild time again) Do you think a properly rebuilt 4.1 (with the correct rods and crank) could handle the power of the turbo setup? My setup would be the same other than that and having the turbo hogged out.

Rick

If you build a 4.1, it will have the correct rods and crank - the 4.1 crank is a rolled fillet design which is the same crank as the 3.8 turbo motors use As for the rods, I would would just use the rods that are in the 4.1 motor.. they are plenty strong enough for the addition of turbocharging.

What I would change, however, is the pistons.. The N/A 4.1s had cast pistons which wouldnt last real long under boost, but you can buy hypereutectic pistons for the 4.1s.... which, while are not really reccomended for a turbo buildup, Jack Cotton HAS run high 10s on Hyperutectic pistons using a stock 1987 109 factory turbo block tho.. I think they CAN be used in turbo applications, so long as you kep a keen eye on ELIMINATING detonation. In other words ZERO knock or detonation!! And running good fuel.

And I doubt your turbo buildup will be 10 second one. Use verything in the 4.1 motor 'cept the pistons would be my guess.. Not sure about wether or not the heads are the same as the 3.8 motors.. maybey someone else can chime in...

 

[83T]

Hey Schlodes,

Actually, I made a mistake on my original build and used hyperutectic pistons, and they have held up well. Had a problem in February where MSD 6BTM stopped functioning, and I have no other form of knock control. Engine pinged so bad (had radio on LOUD and didn't realize) that I trashed a rod bearing. Believe it or not, all cylinders passed a compression check! Pistons held up pretty well, so I might just use them for the 4.1.

As for the rods, I though the 4.1 used the turbo rods?

 

[Schlodes]

Originally posted by 83T

As for the rods, I though the 4.1 used the turbo rods?

I'm pretty sure they are the same.. thats why in my post i said that the only thing really different... would be pistons and that they would need to be changed...

Good luck!

 

[mygrain]

3.8 and 4.1 heads are identical

 

[87regal]

What if you bore the 4.1 over enough to use 350 pistons.

If it is even possible......Someone somewhere mentioned that, I dont know if it is worth it, or even nessacery, but it would open up the choices you have for pistons.

by the way, how far over would u need to go on a 4.1 to use 350 chevy pistons.....if its possible?

 

[b4black]

The 4.1's cylinders are very close together. They are siamesed, meaning two adjacent cylinders share the same wall. I don't think there much room to work with. And not much head gasket material between cylinders.

It's a good idea, but if it would work, I bet plenty of people would already be doing it.

I do remember somebody suggesting something similar with different pistons and rods in a 4.1 (in the General Tech forum).

 

[unboostedV6]

You can bore the 4.1 (3.965" bore) .035" to get the 350 Chevy' 4.000" size, but the compression height is way different, requiring either custom rods, or custom pistons. I chose custom pistons. GB